1. Field of Invention
The invention relates to the field of telecommunications and more specifically to an iterative soft interference canceller (I-SIC) for use on the receiving side of a multi-input multi-output (MIMO) telecommunications system.
2. Description of Related Art
Widespread use of the Internet motivates the design of more reliable, comfortable and efficient communication systems, especially in the mobile environment due to its portability and convenience. So-called the third generation (3G) systems are being introduced to support several hundred kbps data services in addition to high quality voice message transmissions, and its upgraded version, high-speed downlink packet access (HSDPA), is also under discussion and standardization at the third generation partnership project (3GPP) to offer higher bit rate services. However, achievable bit rate is still limited up to 10 Mbps even when HSDPA utilizes automatic repeat request (ARQ) and adaptive modulation and coding scheme (AMCS). However, user demand for data rate requires approximately 100 Mbps to enjoy streaming video, high-speed Internet connection and so forth, even in a mobile situation.
One known strategy to realize high-speed transmission in the physical layer is the expansion of bandwidth. Atarashi, et al., proposed variable spreading factor orthogonal frequency and code division multiplexing (VSF-OFCDM) which assumes 130 MHz bandwidth to achieve 100 Mbps in outdoor environments. However, this approach requires very high speed digital-to-analog and analog-to-digital converter due to its very high sampling rate. Hence, the power consumption, especially in the user equipment, would become a problem. Another problem is that such a wide bandwidth induces excessive multi-path delay, which makes such a suitable receiver difficult to design and operate.
An alternative approach to increasing the spectral efficiency is to adopt higher-order modulation schemes. In fact, IEEE 802.11a employs 64QAM to realize 54 Mbps with 20 MHz bandwidth for indoor wireless local area network (LAN) systems. However, when we consider application of this scheme in the mobile environment, 64QAM would be no longer efficient because it is less tolerant to interference than QPSK. Moreover, greatly increased transmission power would be required to compensate for its poor error rate performance.
On the other hand, spatial multiplexing techniques, for example, the so-called multi-input multi-output (MIMO) system, have gained much attention recently. Information theory results indicate that the capacity of a MIMO system increases linearly with the minimum of the number of transmit antennas and the receive antennas. In MIMO systems, the most serious problem would be interference from other transmit antennas. Foschini, et al., proposed the Bell Laboratories Layered Space-Time (BLAST) architecture to achieve high-speed wireless transmission and the corresponding detection algorithms that employ interference cancellation and suppression. However, this scheme would not be efficient when combined with error correction coding since processing in the detector and the decoder are separately performed. On the other hand, although the maximum a posteriori (MAP) algorithm is known as optimum when jointly operated for detector and decoder, the computational complexity becomes prohibitive.